From e15f431fe2d53cd4673510736da7d4fa1090e096 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski <luto@amacapital.net> Date: Thu, 16 Apr 2015 12:44:47 -0700 Subject: [PATCH] errno.h: Improve ENOSYS's comment ENOSYS is the mechanism used by user code to detect whether the running kernel implements a given system call. It should not be returned by anything except an unimplemented system call. Unfortunately, it is rather frequently used in the kernel to indicate that various new functions of existing system calls are not implemented. This should be discouraged. Improve the comment in errno.h to help clarify ENOSYS's purpose. Signed-off-by: Andy Lutomirski <luto@amacapital.net> Cc: Pavel Machek <pavel@ucw.cz> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Joe Perches <joe@perches.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> --- include/uapi/asm-generic/errno.h | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/include/uapi/asm-generic/errno.h b/include/uapi/asm-generic/errno.h index 1e1ea6e6e7a55..88e0914cf2d99 100644 --- a/include/uapi/asm-generic/errno.h +++ b/include/uapi/asm-generic/errno.h @@ -6,7 +6,16 @@ #define EDEADLK 35 /* Resource deadlock would occur */ #define ENAMETOOLONG 36 /* File name too long */ #define ENOLCK 37 /* No record locks available */ -#define ENOSYS 38 /* Function not implemented */ + +/* + * This error code is special: arch syscall entry code will return + * -ENOSYS if users try to call a syscall that doesn't exist. To keep + * failures of syscalls that really do exist distinguishable from + * failures due to attempts to use a nonexistent syscall, syscall + * implementations should refrain from returning -ENOSYS. + */ +#define ENOSYS 38 /* Invalid system call number */ + #define ENOTEMPTY 39 /* Directory not empty */ #define ELOOP 40 /* Too many symbolic links encountered */ #define EWOULDBLOCK EAGAIN /* Operation would block */ -- 2.30.2